6 Answers
6

A pump can operate continuously to move water between two locations. The wet vac will suck water into the cannister, but you'll need to continuously stop, and dump that water, before it reaches the top of the vacuum. If you're looking at a flooding risk, I'd want the pump.

Thanks, I'm curious about the evacuation of water. What if you just place the body outside of the canister which it usually calls home? I wouldn't expect this to be a continuous proposition, but only in case of emergency.
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mbrownnycAug 29 '11 at 13:05

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@mbrownnyc, Water isn't sucked through the vacuum motor, it's sucked into the canister body via an air vacuum created by the motor on top. The hose it attached to the canister, not the vacuum. I also don't think you'll see a lot of suction power from smaller shop vacs, enough to pull up a spill, but not enough to suck a bucket of water up 5 feet vertically.
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BMitch♦Aug 29 '11 at 13:18

In my experience, most shop vacs -- even the most expensive "contractor-grade" ones -- will not be able to maintain the pipe full of water: you have to suck a mix of air+water or else it will just stall. A trash pump will work the best with large amounts of water (can be rented at any rental place), and a regular sump pump will be the cheapest and most effective option.
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gregmacAug 29 '11 at 22:57

I'm draining my pool cover right now with the shop vac. Run it until the water hits the top. When you pull the lid motor you've already created the suction you need. It is slow but steady. No need to drill a hole in the side. It just pours out the top.

Drill a hole near the bottom of the vac canister and plug it; when the canister is half full remove the plug and water will drain out of the canister but still keep a vacuum as long as water doesn't empty. Size the hole properly: not so small that the canister fills, or so large that it empties too quickly.

About 15 years ago, when I was helping my parents open up their above-ground pool for the summer, we used a small shop-vac to pump the water from the pool cover and dump it onto the lawn. Basically we just took the canister off the vacuum, turned it on, and stuck the hose in the water. The water was moved horizontally, not vertically, so I'm not sure about draining a basement, but the vacuum did operate continuously for some time and didn't seem to be adversely affected.

Not sure they still make any shop vac's like that (didn't realize they ever did). All the ones I've seen connect the hose to the canister. Many also include a float inside the filter space to shutoff the airflow before moisture gets into the motor.
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BMitch♦Aug 31 '11 at 11:37

Some Shop Vacs have a "water pump" feature. You can attach a garden hose to a side port on the vac, and rather than just dumping the water in the canister, it will actually pump the water to another location.